In rail fastenings for fastening rails to wooden ties, the bedplates or ribbed plates, or the ribbed support plates, serve to transfer forces from the rail to the tie or the rail support point and simultaneously to establish the position of the two rails relative to each other such that the required gage for the wheelsets of the trains are maintained at each point of the track.
The bedplates or ribbed plates, or ribbed support plates, thus form a particularly important component of the rail fastening, since horizontal forces are transmited by them from the rails to the rail support points. This means that the bedplates or ribbed plates, or the ribbed support plates, can only be secured against displacement relative to the tie surface or to the abutment surface of the rail support point, and in fact particularly in the direction transverse to the long axis of the track, in that the abutment surfaces of the bedplates or ribbed plates, or of the ribbed support plates, are pressed as a unit, with considerable surface pressure, onto the tie surface or the rail support point by the rail screws or the like, and thus the free horizontal forces acting on the bedplates or ribbed plates, or on the ribbed support plates, can be transmitted as frictional forces, without displacement, to the transverse ties or to the rail support point.
These requirements already existed since the introduction of rail fastenings, the bedplates or ribbed plates, or the ribbed support plates, of which are fastened by rail screws to wooden ties. However, they could not be satisfactorily fullfilled up to now. It has been found in practice that most bedplates or ribbed plates, or ribbed support plates, attain no, or only a small and thus insufficient, frictional contact in the clamped state with the transverse tie or the rail support point, between their abutment face and the rail support point abutment face; and furthermore, this frictional contact becomes increasingly smaller as the period of use of the track equipment increases. It had to be established that in practice a force-transmitting frictional contact between the bedplates or ribbed plates, or ribbed support plates, and the rail support point abutment face, is only attained, with a newly built-in rail support point, in the immediate neighborhood of the rail screw or the like, whether or not this is braced with a spring ring.
This bracing between the bedplates or ribbed plates or ribbed support plates and the tie surface or rail support point abutment face, still readily effective initially, however diminishes considerably even after a short service period, and in fact since plastic deformation of the tie surface occurs due to the high bracing forces. Besides the displacement of the bedplates or ribbed plates, or ribbed support plates, occurring by the action of horizontal forces, with the resulting change in gage, there results the further disadvantage that the walls of the holes in the bedplate or ribbed plate, or ribbed support plates, abut against the shafts of the rail screws and exert bending stresses on the rail screws because of the load resulting from trains on the track, so that the permanent fixed seating of them in the ties is impaired.
Since loosening of the bedplates or ribbed plates, or ribbed support plates, entails a reduction of the overall stability of the track, double or threefold stressing spring washers are also often provided between this and the head of the rail screw. Since, however, such spring washers have not only a small spring path, but also apart from this an unfavorably progressive spring characteristic, their effectiveness is often impaired even by comparatively small plastic deformation of the tie surface. Such spring washers also often break, because of their unfavorable spring characteristic.
It has also been found that when the known rail fastenings are used in combination with wooden ties a very high surface pressure arises about the rail screws, because of which there occurs a plastic-elastic deformation of the tie surface. The disadvantage further results from this that the bedplates or ribbed plates, or ribbed support plates, curve upward in their middle region, and the bedplates or ribbed plates thus lift from the tie surface in the region of the rail.
When traffic passes over the bedplates or ribbed plates, these are transiently pressed down in the curved region--so-called pumping. This pumping then naturally leads to a gradual mechanical destruction of the tie surface. Research has also been undertaken to prevent this so-called pumping of the bedplates or ribbed plates, in fact, by making the bedplates or ribbed plates laid in the region of switches 20 mm thick instead of 16 mm. However, the undesired pumping effect could only be reduced to a small extent by this costly measure.
The most commonly used rail fastening, K-type, initially effects a substantially rigid connection to the bedplate or ribbed plate by the strong clamping of the rail foot by means of hook bolts, clamp plates and spring rings. The so-called lifting wave of the rail which inevitably occurs when the track is used is thus transmitted undamped in the longitudinal direction of the track to the bedplate or ribbed plate. Torsional stresses of the bedplates or ribbed plates and of the transverse ties furthermore result from this in the direction of travel, with the result that plastic deformations of the tie surface occur and again lead to a loosening of the fastening to the transverse tie.
Attempts have in fact been made to remedy this disadvantage by substituting clamp clips or clamps for hook bolts, clamp plates and spring rings. The torsional stresses could in fact be reduced slightly by this means. However, there also simultaneously resulted an undesired reduction of the resistance to through-thrust and twisting.